Hell descended on this city twice: first when it was captured by Islamic State fighters in 2014 and made their capital, and then when it was liberated last year by U.S.-backed forces in a campaign that flattened much of the center of the city.

Photos and videos show the damage here, but they don’t prepare you for the intensity of the destruction. Buildings are pulverized into rubble, block after block. Reconstruction in some areas is a distant prospect. It will take years just to clear away the shattered concrete and jungle of twisted rebar.

Raqqa experienced a ferocity of urban combat rarely seen since World War II. Think of newsreels of Stalingrad in 1943 or Berlin in 1945. Those cities are symbols of the fury of war and the cost of liberation, and Raqqa should be, too.

Raqqa’s liberators were members of the Syrian Democratic Forces, a Kurdish-led militia that captured the city one building at a time. They surrounded Raqqa in late June and then squeezed it, ever tighter, until October, when resistance finally collapsed. Brave as they were, the SDF fighters couldn’t have won without devastating fire support from U.S. warplanes, armed drones and artillery. It was a brutally effective combination. One of the last redoubts was the local hospital.

The Islamic State left a farewell message: The city is laced with IEDs, which have injured nearly 500 people since October, including more than 150 children.

Some unforgettable images emerged during a day-long tour of the city last week with U.S. Special Operations forces who directed the campaign: mass graves dug in a public amphitheater to intimidate adversaries, the midtown traffic circle where the Islamic State videoed its grisly executions for the Internet; the stadium where the jihadists tortured prisoners in underground dungeons. The Islamic State made the city a theater of death.

People here try to express the horror of those days, but what’s most telling is the distant, hollow look in their eyes. “If you didn’t need something, you didn’t go outside,” says a weathered man named Abu Basser, standing in front of the ruined building that was once the Islamic State’s administrative headquarters. “We saw the darkest days of our lives.”

On the street in front of him, a few yellow taxis are flitting by. Bus service has just resumed. Perhaps 50,000 people, a sixth of Raqqa’s former population, have returned.

We stop in Mishlib, a neighborhood in the eastern district of the city. Two ladies pull out plastic chairs from their house, and a little crowd gathers on the sidewalk. Sajida, a hauntingly pretty 10-year-old dressed in a turtleneck and ripped jeans, hugs a female U.S. Army officer in tan camouflage; Ahmed, 20, a cigarette glowing at his lips, remembers the days when the Islamic State cut off people’s fingers if they smoked. He tries a laugh.

“The children were living a nightmare,” says one of the mothers, who’s still worried enough about the jihadists that she doesn’t want to give her name. “They were taught how to kill.” Near her is a little girl in pink sneakers and a sky-blue sweatshirt that says “Goofy” and, close by, a boy in a Gap jacket making funny faces. Looking at their smiles as they cluster for photographs, you think: Whatever they lived through, they’re not frightened now.

What are the lessons of Raqqa? One is that the United States fulfilled its commitment of 2014 to “degrade and ultimately destroy” the Islamic State. The conquest of its capital, however chilling, demonstrates the much-doubted quality of U.S. resolve. The U.S. military’s strategy here was “annihilation,” and it meant it. The next time, adversaries should be warier of picking a fight.

Another moral is that it’s a mistake to let a determined adversary like the Islamic State ever gain control of an urban center like Raqqa, or Mosul in Iraq, which was also cratered in its liberation. Once committed fighters take over a city, they can be rooted out only at great human cost.

And finally, Raqqa is a warning to be careful about destroying the ruling order, anywhere, without knowing what will come next. Russian President Vladimir Putin keeps making this point — the United States was reckless to encourage the overthrow of authority in Syria, Iraq, Yemen and Libya without better planning for the “day after” — and he’s probably right. Too often, the vacuums have been filled by warlords, foreign mercenaries and death cults.

The United States and its allies nearly destroyed Raqqa to rescue it from a caliphate that governed by torture. It was a just war, but we should try hard to avoid having to fight one like it again.